“Although much attention was focused on spills from oil and gas operations, it is reassuring the sampling shows no evidence of oil and gas pollutants,” said Dr. Larry Wolk, the department’s executive director and chief medical officer. “There were elevated E.coli levels, as we expected, in some locations.”

“What we’ve really seen is this kind of slow trickle of smaller spills, and all are specifically related to the flood,” said Mr. Allen, as reported by Energy in Depth. “It wasn’t user error or improper operations; it all falls in the act-of-God category.”

Anti-fracking groups fueled dozens of media reports and online posts declaring that the floods had released toxic levels of oil, gas and fracking fluid into Colorado’s waterways, even though state and industry officials said repeatedly that no hydraulic fracturing was taking place at the time.

“We’re talking about tens of thousands of toxic chemicals floating down the river, potentially ending up in communities, next to homes, next to agriculture land,” said Sam Schabacker of Food & Water Watch told Northern Colorado Community Radio in a Sept. 27 report. “We are just beginning to see the extent of the devastation.”

The Colorado Oil and Gas Conservation Commission reported Tuesday that crews are tracking 13 notable releases of oil totaling 43,134 gallons, an amount of seepage that is expected to be dissipated by rushing rivers and streams.

Gov. John Hickenlooper, a Democrat, described the spills last month as “very small relative to the huge flow of water coming through.”

A greater concern for public-health officials is the estimated 220 million gallons of raw and partially treated sewage that poured into waterways during the flooding.

The department collected 29 samples from eight rivers affected by the flooding. While the study found no sign of oil and gas pollutants, high levels of E.coli bacteria were found in the Boulder Creek and Big Thompson River watershed.

“E.coli indicates human and animal bacteria from untreated sewage that can make people sick,” the department said in its statement. “However, outbreaks of communicable diseases or illnesses after floods seldom are seen and have not been reported with the recent flooding in Colorado.”